Pressure lock grounding outlet



R. L. MARTIN PRESSURE LOCK GROUNDING OUTLET Aug. 29, 1967 2 Sheets-Sheet1 Filed Dec. 11, 1964 INVENTOR ROBERT LEWIS MARTIN ATTORNEY Aug. 29,1967 PRESSURE LOCK GROUNDING OUTLET Filed Dec. 11, 1964 2 Sheets-Sheet73 FFGZ I00 52 4s 44 us 400 96 I2 76 74 54 E I 54 28 76 74 z w. I g 43 al 108 I00 K5 I06 "I V 28 FIGS INVENTOR ROBERT LEWIS MARTIN ATTORNEY R.1.. MARTIN 3,339,170-

United States Patent 3,339,170 PRESSURE LOCK GROUNDING OUTLET Robert L.Martin, Cranston, R.I., assignor to General Electric Company, acorporation of New York Filed Dec. 11, 1964, Ser. No. 417,740 7 Claims.(Cl. 339-31) ABSTRACT OF THE DISCLOSURE This invention relates to agrounding outlet having multiple spring-operated wire fastening meansfor providing electrical engagement with inserted line wires ofdifferent sizes. More specifically, it relates to a duplex plugreceptacle having a pair of electrical line contacts each having springoperated wire gripping means adapted for gripping several line wires ofdiiferent sizes.

The performance of prior art duplex plug receptacles which have beenprovided with spring type wire fastening means has been less thansatisfactory where two or more wires of different sizes are fastened andit is desired to release only the larger of the wires while the smallerwire is under tension. The gripping elements of these spring typefastening devices have been designed in various ways, but these priordesigns have been deficient in a number of respects. One principaldefect is observed when line wires of diiferent sizes are employed andthis has also been found to be the case where wires of the same size areinserted.

Where an attempt is made to remedy this deficiency by utilizing abifurcated spring to provide two spring locking elements for a fasteningarrangement, this arrangement has also proven less than satisfactory inactual use in holding two wires of the same or different sizes. Thisarrangement is especially deficient during the releasing of the wires inthat it is not possible to release only one of the wires withoutsimultaneously releasing the other where both are held by the samespring element even though it is bifurcated where deflection of oneprong of the spring serves to impart a similar deflection to the otherprong.

Surprisingly it has been found, however, that it is possible to providehighly effective spring action where two wires are held by two portionsor two locking tongues of a single spring element. In fact, it has beenfound that in accordance with the present invention, the pressure on afirst wire which is held by a first locking tongue of a single springelement is increased rather than decreased when the pressure on a secondwire, held by a second locking tongue of the same spring element isdecreased.

It is an object of this invention to provide a convenience electricaloutlet in which a plurality of electrical supply wires of differentsizes will be firmly grasped simply on insertion of the wires.

It is another object of this invention to provide a de vice in which thesimple pushing in of a plurality of supply wires establishes soundelectrical contact with the contact elements for supply of heavyelectrical loads from one of said wires to another.

It is another object of this invention to provide such a device in whicha single electrical contact member is readily connectable with two ormore electrical supply wires of different sizes.

It is a further object of this invention to provide an insulatinghousing for such a device so that the spring elements which engage asupply wire are enclosed in separate insulated pockets formed as anintegral part of the insulating housing.

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Still another object is to provide a device in which wires can beconnected by push in techniques to carry relatively heavy electricalloads.

In one of its broader aspects, the article of the present inventioncomprises a push-in type of electrical connector having a pair of leafspring locking tongues disposed as the outer prongs of an E form,

holding means for limiting the flexural movement of the central prongwhen an outer prong is flexed,

holding means for limiting rotational or linear motion of said E form inthe plane of said form,

the connecting arm of said E form being free to serve as a forcetransmitting lever operating about the center prong as a fulcrum toimpart counterfiexing force to one outer prong when flexing force isapplied to the other outer prong.

In another of its aspects a number of the objects are accomplished inaccordance with this invention by providing a convenience electricaloutlet for use with a grounding attachment plug to have a groundingcontact and two shallow U-shaped line contacts, each U-shaped linecontact of which is provided with arms terminating in prong receivingmeans and each U-shaped line contact of which is also provided in thebase thereof with four separate cam arrangements for engaging fourseparate wires in a springlock arrangement in the base of each contact.

To provide the four separate cam arrangements, the line contacts areformed from metal strip having good leaf spring property and the stripis trifurcated at two longitudinal portions of the base of the linecontact so as to form three parallel prongs or legs extending lengthwiseof the contact. One end of each of the outer legs is made free of thebase so as to form a cantilevered cam leg. The two outer cam legs incombination with the central leg and the portion of the strip whichjoins the three legs at their held end comprises an E form which isintegrated into the contact as one component element thereof.

Each of the cam legs may be bent up from the base of the U-shapedcontact so that a wire may be pushed through the opening in the baseformed by the bending up of the end of the cam leg. A wire may thus beengaged in the base of the contact between the free, movable end of thecam leg and the remaining edge or shelf of the contact base from whichthe free end was displaced. An inserted wire is electrically contactedon one side by the shelf and onthe other side by the free end of theleg. Four wires can therefore be individually held in firm engagementwith such a U-shaped line contact.

The line contacts are enclosed within an insulating housing which isformed by two molded insulating members. One of these members, a base,is provided with a pair of pockets, each of which snugly receives one ofthe U- shaped line contact strips. Elongated ribs are provided on thesecond housing member, a cover, to hold the line contacts firmly againstthe base when the base and cover are in the assembled position.

Each line contact is also provided with a pair of breakolf tabs wherebyeach contact can be made into two separate pieces, each of which can beconnected to two wires of different sizes for split-circuit wiring. Theelongated ribs also partially divide the pair of pockets so as to beinterposed between the cam legs of each of the separate pieces.

Other objects and further details of that which is believed to be novelin the articles of the present invention will be clear from thefollowing description and claims taken with the accompanying drawingswherein:

FIG. 1 is an exploded view of a grounding outlet constructed inaccordance with this invention and incorporating the E form springlocking element.

FIG. 2 is a side view of the grounding outlet with portions broken awayand others shown in sections.

FIG. 3 is a portion of a side view of the grounding outlet with portionsshown in section.

FIG. 4 is a portion of a rear view of a grounding outlet with a portionof the base broken away.

FIG. 5 is a portion of a side view of a grounding outlet with a portionshown in section taken along the line 1-1 in FIG. 3, to reveal a pair ofbreak-01f tabs.

By reference to FIG. 1, it will be seen that a grounding outletconstructed in accordance with this invention comprises six principalcomponents. A molded cover 2 is shown with a grounding contact 4 and aline contact 6 assembled thereon. Shown in spaced relationship withrespect to cover 2 is a mounting bracket 8, a second line contact 10,and a molded base 12.

Referring now to line contact 10, which is identical to line contact 6,it will be seen that the line contacts are each formed from a singlepiece of metal, preferably a spring tempered brass, and are generally ofa shallow U- sha e. Each arm of the U-shape contact is formed to provideprong receiving means 14. The prong receiving means 14 are trifurcatedportions of the contact, and comprise three legs 16, 18, and 20. Legs 16and 18 are parallel, and the third leg 20 is perpendicular to them. Thethree leg arrangement provides a double-wipe arrangement for engagingthe prong of a connector. This double- Wipe is provided with either theparallel prongs of a 125 volt plug, or with the in line arrangement ofthe prongs of a 220 volt plug. It is necessary to use a different coverwhen changing voltages, for the aperture for the prong must be formeddifferently. However, the single device is adapted for use at aplurality of voltages by appropriate change of the cover element.

The base 22 of the U-shaped line contact is generally rectangular inshape. Two spaced portions of the base are trifurcated so as to formlegs 24, 26, 28, 30, 32, and 34. The outer legs 24, 28, 30, and 34 areeach cut free of the base at one end and partially bent so as to formcantilever cam legs. A channel 35 is shown to be coined in the center ofeach of the legs 24, 28, 30 and 34 extending the length of the leg toadd strength to the cantilever cam legs. The legs 24, 28, 30, and 34 arealso bent at points 36, 38, 40, and 42, respectively, so that the freeends of the cam legs extend out of a plane of the base 22 in thedirection of the prong receiving means 14. Central leg 26 separates thecam legs 24 and 28 from each other and mechanically joins their heldends to a central portion 44 of the base 22. Similarly, cam legs 30 and34 are separated from each other and mechanically joined to the centralportion 44 of the base by center leg 32. The central portion 44 isformed with a rectangular aperture 46 therein, and with a pair ofbreak-off tabs 48 and 50 on either side of the aperture. These break-offtabs 48 and 50 are bent out of the plane of the base to make them moreaccessible when it is desired to break them off, as will be laterdescribed.

Referring to molded cover 2, and line contact 6 in FIG. 1, thepositioning of the line contacts 6 and with respect to the cover will beunderstood. The features provided on the cover 2 for the mounting ofline contact 10 are the mirror image of those for the line contact 6which is shown in its operative position. Furthermore, in the duplextype plug receptacle or outlet which is shown, the line contacts arepositioned symmetrically with respect to perpendicular axes drawnthrough the center of the outlet and extending in directions parallel tothe length and width of the outlet respectively. The cover 2 is providedwith elongated ribs 52 and 54 extending in the direction of the centerlegs and upon which rest the center legs 26 and 32 of the line contact.These elongated ribs 52 and 54 also serve as insulating barriers betweenthe cam legs. A locating projection 56 extends through the rectangularaperture 46 formed in the line contact.

Before discussing the wire fastening arrangement of the duplex plugreceptacle illustrated in FIGS. 1 through 5, the remainder of thereceptacle assembly shown in FIG. 1 will be discussed.

Wells 58 and 60 are provided in the cover 2 for accepting the prongreceiving means 14 of the line contacts. Apertures 62 and 64 areprovided in the cover in alignment with the wells 58 and 60,respectively, for the insertion of plug prongs which engage the prongreceiving means 14.

The grounding contact 4 shown positioned on the cover 2 is provided withtwo double-wipe prong engaging portions, one of which is shown at 66.The double-wipe prong engaging portion which is shown includes thecontact members 68 and 70. The mounting bracket 8 which is provided withthe usual mounting means at either end is positioned on the molded coverin abutting relationship with the grounding contact 4, and in insulatedrelation between the line contacts 6 and 10. The molded base 12 isplaced over the line contacts 6 and 10 and the mounting bracket 8. Theedge 72 of the cover 2 engages an edge of the base. This edge is on thehidden side of the base in FIG. 1.

Referring to FIG. 2, it will be seen that the base 12 is provided withan insulating wall or barrier 74 which ex tends lengthwise of the baseand divides the base into two pockets, each of which has a rectangularshape conforming to that of the base 22 of the U-shaped line contacts 6and 10. The back wall 76 of the base 12 engages the base 22 of the linecontacts, holding the center legs of the contacts 6 and 10 in engagementwith the elongated ribs 52 and 54. The end of the wall 74 which projectsaway from the back wall 76 engages the mounting bracket 8 securing itand the grounding contact 4 between the base 12 and the cover 2. Afterthe six major components shown in FIG. 1 are assembled, they are heldtogether by a pair of screws. These screws pass through the holes 78 and80 in the molded base, and holes 82 and 84 in the mounting bracket andengage threaded holes in the cover 2, one of which (86) is shown.

Refering now to the detail sectional views in FIGS. 2, 3 and 4 alongwith the exploded view in FIG. 1, the wire fastening means of the duplexoutlet shown will be understood. On both sides of the elongated ribs 52and 54 are formed identical shelf portions 88. Each of these shelfportions is provided with a wire receiving bore 90. As is best seen inFIGS. 2 and 3, this bore 90 is provided with a chamfered lead 92, and aconical end 94. The chamfered lead 92 aids in guiding a wire into thebore, and the conical end 94 serves as an. inclined surface or ramp fordeveloping a wedging action as explained below, and the conical end alsoaids in centering the wire which is gripped by the fastening means.Extending from each shelf 88 is a rib 96 which has a groove 98 formedtherein. This groove can be tangent with a portion of the perimeter ofthe bore 90 to aid in directing a wire into the bore.

Base 12 is provided with eight identical holes 100 through which wiresare inserted to be engaged by the spring lock fastening means. Two ofthese holes 100 are shown in cross-section in FIGS. 2 and 3. As can beseen by making reference to FIGS. 2 through 4, the edges or shelves 102,from which the free ends of the cam legs are severed, extend into theprojection of the holes 100. Also, the free ends 104 of the cam legsextend within the projection of the holes 100. A wire upon beinginserted in a hole 100 may first engage shelf 102, and may be deflectedby it to engage the inclined surface of free end 104 of a cam leg as itis further inserted.

Although the shelf 102 extends into the projection of hole 100, it doesnot extend so far as to prevent free insertion of the wire past theextending portion of shelf edge 102 and directly into contact with thedefiectable cam leg end 104.

The end of an inserted wire can ride down the inclined surface of theend of cam leg 104 until it reaches its furthest extent of entry beforethe cam leg end 104 is deflected. At this point the wire will contactthe inclined surface leg end 104, shelf edge 102 and the upper edge ofthe side of hole 100 diametrically opposite shelf edge 102.

Pushing the wire causes the leg end 104 to deflect and allows the wireto contact the surface of rib 96. Surface 96 then becomes a thirdcontact point on the wire in place of the edge of hole 100. Furtherinsertion of the wire in the hole causes it to engage the groove 98 inthe rib 96. It may then ride up and over an inclined surface such as acontinuation of chamfered lead 92 through groove 98 before being guidedinto the bore 90. The wire is centered in the bore 90 by the conical end94.

Another important aspect of the novel gripping means of this inventionis described with reference to FIGURE 3. On the right side of FIG. 3, awire is shown engaged by the spring-lock fastening means. As the wire isinserted in the hole 100 and presses against the free end 104 of the camleg, the cam leg is deflected in cantilever fashion throughout itslength, thereby providing spring bias force on the side of the wire.Aiding in providing a resilient bias on the free end of the cam leg andgiving more yieldability to the cam leg is a torsional spring forceprovided by the center leg 26 or 32. As is shown in FIG. 2, a portion ofthe center legs 26 and 32 of the base 22 of the U-shaped contact is heldin firm engagement with the back wall 76 of the molded base 12 by theelongated ribs 52 and 54. The elongated ribs can be made to engage thecenter legs 26 and 32 only along a relatively short length and along anarrow area. Engagement along a narrow central area is accomplished bymaking the elongated ribs 52 and 54 half-rounded, as best seen inFIG. 1. With this construction the insertion of a wire in the springlockfastening means not only causes deflection of the yieldable cam legs,but also causes a torsional deflection or yielding of the center legs 26and 32 which aids in providing a spring bias force upon the wire. Theline like contact between the half-rounded edges of the elongated ribs52 and 54 and the center legs 26 and 32 provides a pivot line or fulcrumfor torsional deflection of the center legs. Use of this fulcrum canalso confine the deflection largely to the cam legs and the associatedcenter leg, where it is desired to immobilize or otherwise preventmovement of other parts of the line contact. Such immobilization can beaccomplished whether one or both of the cam legs adjacent a center legare utilized in gripping a wire. The cam legs are also confined betweenthe elongated ribs 52 or 54 and either the outer walls or dividing wall74 of the base 12 which prevent deflection of the cam legs other thanthat which is desired.

Rectangular apertures or access holes 106 are provided for the insertionof a tool to release the pressure-lock wire fastening means. A tool suchas a screwdriver 108 as shown in FIG. 3 is inserted through arectangular aperture 106 and is brought to bear on the cam leg 34,thereby deflecting the cam leg away from the wire 110 and releasing thewire. Surface 112 of shelf 88 is engaged by the free end 104 of the camleg before the leg is deflected beyond its elastic'limit, therebypreventing permanent damage of the contact when a wire is released.Where the advantage of increased contact pressure is sought on the camleg opposite that deflected for release of a wire, the'rib supportcan'preferably extend tothe region of the contact strip at which therelease pressure is to be exerted.

As previously mentioned, the line contacts are provided with break-01ftabs 48 and 50 in case it is desired to form two separate contact piecesfrom each line contact for split-phase wiring. The molded base 12 isprovided with fracturable wall portions 112 which cover the break-offtabs. These wall portions prevent shorting of the break-off tabs beforethey are removed. The vertical walls 114 and the horizontal walls 116which enclose the break-off tabs 48 and 50 are best seen in FIG. 5. Inorder to provide split-phase wiring, the wall portions 114 and 116 arebroken away to expose the break-off tabs 48 and 50.

After breaking away these wall portions the tabs 48 and 50 are eachgrasped by a tool such as pliers and broken away from the centralportion 44 of the line contact. The separate pieces are firmly heldwithin the housing comprising the molded cover 2 and the molded base 12during and after removal of the break-off portions by the portion 118 ofthe base which holds the central portion 44 of the contact in firmengagement with the elongated rib 54 of the cover. Each piece is heldwithin a well formed by the side walls of the base 12 and the centralwall 74 which divides the base into two pockets. Also, the center leg 26or 32 of each separate piece is held against the molded base 12 by theelongated ribs 52 and 54 respectively.

It has thus been seen that in one of its narrower aspects this inventiondiscloses a double grounding outlet in which each of the line contactsis formed from a single sheet of spring tempered brass. Four separatespring-lock wire fastening means are provided on each line contact.Whereas the four spring-lock wire fastening means are separate, it ispossible to connect four wires of different size-s to each line contact.Furthermore, by providing the line contacts with a pair of break-offtabs it is possible to separate the line contacts into two separatepieces, each of which can be connected to two wires of different sizes.

While a particular embodiment of the invention has been shown, otherembodiments of the invention will be apparent to those skilled in theart, and it is intended to cover by the appendant claims all theembodiments falling within the scope thereof.

One of the more important features of the device of the presentinvention relates to the facility with which the device may be used inthe field as a versatile tool for the rapid wiring of a variety ofcircuits. In part, this is due to the inclusion of four separatelyoperable cam legs, all of which are electrically joined for each contactstrip used in the device. Where the device is not used for the wiring ofseparate circuits to the two electrically separable outlets, it isevident that the four wire gripping cam legs can accommodate and providejunction connection among four wires of different dimensions in anycombination. For example, where the electrical supply from a firstsupply line to the outlet is made with a number 10 gauge wire, thedevice may be wired by the insertion of the stripped wire ends directlyinto holes in the rear of the device so that one supply wire of the lineis gripped by each of the contact strips. If the electrical supply for aceiling fixture is to be obtained from the circuit already connected tothe outlet, this may be accomplished by simply inserting the strippedends of the wire which might be of a number 12 gauge into theappropriate pair of holes 100 in the reverse of the outlet.

Similarly, if a clock outlet is to be wired from the same outlet device,a number 14 wire may be connected in the outlet by the insertion of itswire ends into appropriate holes in the reverse side of the device.

While each of these wires is held firmly in place, if some change in thewiring should be found necessary, this may be accomplished simply by useof the release mechanism by inserting an instrument into the appropriatehole 106 adjacent the wire to be released and only that wire will bereleased which is held by the specific cam leg acted on by theinstrument inserted through the hole.

One highly useful modification of the device of the present inventionwhich illustrates its capabilities as a wiring device for the quick easywiring of a variety of electrical circuits is that which employs onlythe wire gripping portions of the contact strips such as 6 and 10 ofFIGURE 1. These portions comprise two E-forms face to face and joined bytheir central legs to a shelf Strip.

In this modification the prong receiving ends may be omitted and thespacing between the parallel strips may be reduced to provide a verycompact unit having an insulating barrier between the contact strips.The unit produced by this modification is very compact and is usefullymounted on the inside of the cover of a junction box to provide meansfor rapid connection of four wires to each of two contact strips. Anoperating device of this construction had a housing for containing thecontact strip which housing was two inches long, one inch wide andslightly over one half inch deep.

Alternatively a junction box push in type connector can be provided withthree parallel contact strips, each being adapted for push-in connectionof four wires. Such a connector can be supplied with 220 volt power byconnecting two wires supplying the 220 volt power to two of the threecontact strips, and connecting a third wire at an intermediate supplyvoltage to the third contact strip. For example, the two wires havingthe 220 voltage level between them can be connected to the two outercontact strips, and the third wire at the intermediate voltage can beconnected to the center of the three parallel contact strips.

By then making push-in connections of one set of two wires to one outerand the center strip respectively and by making separate push-inconnections of a second set of two wires to the center and the otherouter strip respectively, two separate 110 volt circuits can be rapidlyand securely connected in the junction box through the three stripjunction unit.

Also longer strips having more than two pairs of cam legs or having camlegs with different orientation are contemplated within the scope ofthis invention.

As a separate unit incorporated into the junction box, an insulatedgrounding strip equipped to be connected by screw terminals can bemounted in insulated relation with the cover of the box on which thejunction box itself is mounted or it can be mounted in integral fashionwith the insulated housing of the junction box itself.

One of the advantages of the present invention derives from the betterelectrical contact which is established between the stripped copperconductor and the electrically contacted edges of the contact strip.This better contact is the result of the development of a contactpressure which is quite high for the effort needed to establish thepressure. This pressure is developed through a novel combined pinchingand wedging action as the conductor passes over a guiding surface suchas the surface of rib 96. This surface receives the wire, and at thesame time the wire is pinched between the two edges 102 and 104.

Referring particularly to FIGURE 3, it will be seen that the free end104 on one side of the wire acts to pinch the wire between the surface98 and the contact edge 102 of the shelf on the other side of the wire.The relation of these three surfaces is shown more clearly in FIGURE 2which illustrates the position of the three surfaces before the wire endis pushed into place for establishing electrical contact. As is evident,the shelf edge 102 protrudes out slightly beyond the closest portion ofthe hole 100, i.e. the edge 102 is positioned closer to the axis of thehole 100 than the portion of the vertical surface above the edge 102.

Surface 98 serves to provide a wedging action in guiding the wire end asit rides over this surface during the pushing in of the stripped wire.This is particularly evident as the wire end rides up the inclinedsurface of the conical end 94.

The contact strip is not held in a completely immovable fashion so thatas the bared wire is pushed into place there is a slight movement of thecontact strip back and forth as the need arises. However, the latitudeof movement of edge 102 does not permit it to move to a position wherethe shelf will not intersect a straight line between the portions of thesurfaces 100 and 98 closest to the center of the outlet. Also, as may beseen from FIG. 4, the distance from one of the two exposed shelf edges102 of the contact strip to the other edge 102 is longer than thedistance between the most closely spaced sides of holes 100. The resultof the exposure of the edge 102 in each hole 100 coupled with theguiding action of the surface of fin 96 is a wedging action of theentering wire against the edge of free end 104 after the wire is broughtinto contact with the edge of end 104 by deflection of the end.

The improved electrical contact results in part because the two edges102 and the edge of end 104 are both urged into contact with thestripped copper conductor but at higher pressures than those achieved byother devices which permit such easy entry of the conductor.

A unique wire locking mechanism is accordingly provided pursuant to thisinvention from a single strip of material forming the contact because ofthis combination of ease of the push-in entry of the wire and firmnessof gripping the wire at higher contact pressure.

What is claimed is as follows:

1. A push-in type electrical connector disposed in a housing, saidconnector comprising a pair of conductive leaf spring locking tonguesdisposed as the outer prongs of an E-form, holding means on said housingfor limiting the flexural movement of the central prong when an outerprong is flexed, further holding means on said housing for limitingrotational or linear motion of said E-form in the plane of said form,the connecting arm of said E-form being free to serve as a forcetransmitting lever operating about the center prong as a fulcrum toimpart counter flexing force to an outer prong when flexing force isapplied to the other outer pron-g.

2. The connector of claim 1 in which the center prong of the E form isjoined to a cross member portions of which are disposed proximate thefree ends of the outer prongs so that a tensile force is developed insaid center prong when a separative force is applied between one of thefree ends and a portion of said cross member.

3. The connector of claim. 2 in which said E form and joined crossmember are formed from a single piece of conductive metal.

4. The connector of claim 1 in which a plurality of E-forms areelectrically joined by their central prongs.

5. The connector of claim 4 in which the joined E- forms are fashionedof a single piece of metal.

6. The connector of claim 5 in which the free ends of the E-form outerprongs are confronted with a cross piece attached at the central prong.

7. The connector of claim 6 in which the strip has weakened portions inthe cross pieces adapted to be broken to separate said strip into aplurality of portions each having at least one E-form.

References Cited UNITED STATES PATENTS 2,944,242 7/ 1960 Bentley 339-2,969,518 1/1961 Slater 339-31 MARVIN A. CHAMPION, Primary Examiner.PATR K A.- C IFFOR x n

1. A PUSH-IN TYPE ELECTRICAL CONNECTOR DISPOSED IN A HOUSING, SAIDCONNECTOR COMPRISING A PAIR OF CONDUCTIVE LEAF SPRING LOCKING TONGUESDISPOSED AS THE OUTER PRONGS OF AN E-FORM, HOLDING MEANS ON SAID HOUSINGFOR LIMITING THE FLEXURAL MOVEMENT OF THE CENTRAL PRONG WHEN AN OUTERPRONG IS FLEXED, FURTHER HOLDING MEANS ON SAID HOUSING FOR LIMITINGROTATIONAL OR LINEAR MOTION OF SAID E-FORM IN THE PLANE OF SAID FORM,THE CONNECTING ARM OF SAID E-FORM BEING FREE TO SERVE AS A FORCETRANSMITTING LEVER OPERATING ABOUT THE CENTER PRONG AS A FULCRUM TOIMPART COUNTER FLEXING FORCE TO AN OUTER PRONG WHEN FLEXING FORCE ISAPPLIED TO THE OTHER OUTER PRONG.